1. Technical Field
The present invention relates to an illumination device and a projector.
2. Related Art
There has been known an illumination device provided with a solid-state light source such as a semiconductor laser and a phosphor layer for generating fluorescence using light emitted from the solid-state light source as excitation light. In JP-A-2013-250494, for example, there is disclosed a light source device provided with a semiconductor laser source, a light separation element, a fluorescent element, a first reflecting element, a quarter-wave plate, a diffuser plate, and a second reflecting element.
In this light source device, the excitation light emitted from the semiconductor laser source enters the light separation element, and is separated into two light beams by the light separation element having a polarization separation property. The fluorescent element is irradiated with one of the light beams separated from by the light separation element as the excitation light, and thus the fluorescence is emitted. The fluorescence is reflected by the first reflecting element toward the light separation element, and is then emitted to the outside via the light separation element. The other of the light beams separated by the light separation element is adjusted by the quarter-wave plate in the polarization state, and is then diffused by the diffuser plate in the state in which the polarization is maintained, and at the same time, reflected by the second reflecting element toward the light separation element via the quarter-wave plate, and then emitted to the outside via the light separation element.
In the light source device of JP-A-2013-250494, the light beam, with which the phosphor layer is not irradiated, and which is emitted to the outside, out of the light beams emitted from the solid-state light source is diffused by the diffuser plate for the purpose of homogenizing the illuminance distribution and at the same time resolving the speckle noise. In order to make use of the diffused light with high efficiency, for example, when right circularly polarized light is diffusely reflected by the diffuser plate and the reflecting plate, it is necessary for the right circularly polarized light to be converted into left circularly polarized light. However, if the diffusion angle of the light by the diffuser plate is increased, the polarization retention rate drops. If the polarization retention rate drops, the amount of the light to be emitted to the outside via the light separation element decreases. In other words, the efficiency of the diffused light drops. Therefore, in order to obtain the polarization retention rate equal to or higher than 95%, the diffusion angle is set to be equal to or smaller than 13°. However, at this level, diffusion of the light is not sufficient, and the effect of homogenizing the illuminance distribution and the effect of remediating the speckle noise cannot sufficiently be obtained.
Further, the configuration for setting the diffusion angle of the diffuser plate to be equal to or smaller than 13° is not specifically described. If the diffusion angle of the diffuser plate is too small, there is a problem that color unevenness occurs due to an increase in the difference between the diffusion angle of the blue light and the diffusion angle of the yellow light. Therefore, the diffusion angle of the diffusely reflecting element needs to appropriately be set.